A Solar Grand Plan  

Scientific American has a reasonably ambitious plan to derive a large part of the energy required by the US from solar power by 2050, which they deem "A Solar Grand Plan". The point out this could end US dependence on foreign oil and slash greenhouse gas emissions (though there would still be more work required to slash greenhouse emissions by the required amount). They put more emphasis on photovoltaic power plants compared to CSP power plants than I would prefer - I would have thought getting PV on as many rooftops as possible (at least in the sun belt) would be the best bet and leave CSP for large scale generation out in the deserts.

Key Concepts

* A massive switch from coal, oil, natural gas and nuclear power plants to solar power plants could supply 69 percent of the U.S.’s electricity and 35 percent of its total energy by 2050.
* A vast area of photovoltaic cells would have to be erected in the Southwest. Excess daytime energy would be stored as compressed air in underground caverns to be tapped during nighttime hours.
* Large solar concentrator power plants would be built as well.
* A new direct-current power transmission backbone would deliver solar electricity across the country.
* But $420 billion in subsidies from 2011 to 2050 would be required to fund the infrastructure and make it cost-competitive.

Introduction


Well-meaning scientists, engineers, economists and politicians have proposed various steps that could slightly reduce fossil-fuel use and emissions. These steps are not enough. The U.S. needs a bold plan to free itself from fossil fuels. Our analysis convinces us that a massive switch to solar power is the logical answer.

Solar energy’s potential is off the chart. The energy in sunlight striking the earth for 40 minutes is equivalent to global energy consumption for a year. The U.S. is lucky to be endowed with a vast resource; at least 250,000 square miles of land in the Southwest alone are suitable for constructing solar power plants, and that land receives more than 4,500 quadrillion British thermal units (Btu) of solar radiation a year. Converting only 2.5 percent of that radiation into electricity would match the nation’s total energy consumption in 2006.

To convert the country to solar power, huge tracts of land would have to be covered with photovoltaic panels and solar heating troughs. A direct-current (DC) transmission backbone would also have to be erected to send that energy efficiently across the nation.

The technology is ready. On the following pages we present a grand plan that could provide 69 percent of the U.S.’s electricity and 35 percent of its total energy (which includes transportation) with solar power by 2050. We project that this energy could be sold to consumers at rates equivalent to today’s rates for conventional power sources, about five cents per kilowatt-hour (kWh). If wind, biomass and geothermal sources were also developed, renewable energy could provide 100 percent of the nation’s electricity and 90 percent of its energy by 2100.

The federal government would have to invest more than $400 billion over the next 40 years to complete the 2050 plan. That investment is substantial, but the payoff is greater. Solar plants consume little or no fuel, saving billions of dollars year after year. The infrastructure would displace 300 large coal-fired power plants and 300 more large natural gas plants and all the fuels they consume. The plan would effectively eliminate all imported oil, fundamentally cutting U.S. trade deficits and easing political tension in the Middle East and elsewhere. Because solar technologies are almost pollution-free, the plan would also reduce greenhouse gas emissions from power plants by 1.7 billion tons a year, and another 1.9 billion tons from gasoline vehicles would be displaced by plug-in hybrids refueled by the solar power grid. In 2050 U.S. carbon dioxide emissions would be 62 percent below 2005 levels, putting a major brake on global warming. ...

The Energy Blog points out that solar cell production increased by 50% last year.

According to The Earth Policy Institute production of photovoltaics (PV) jumped to 3,800 megawatts worldwide in 2007, up an estimated 50 percent over 2006. At the end of the year, according to preliminary data, cumulative global production stood at 12,400 megawatts, enough to power 2.4 million U.S. homes. Growing by an impressive average of 48 percent each year since 2002, PV production has been doubling every two years, making it the world’s fastest-growing energy source.

A key force driving the advancement of thin-film technologies is a polysilicon shortage that began in April 2004. In 2006, for the first time, more than half of polysilicon production went into PVs instead of computer chips. While thin films are not as efficient at converting sunlight to electricity, they currently cost less and their physical flexibility makes them more versatile than traditional solar cells. Led by the United States, thin film grew from 4 percent of the market in 2003 to 7 percent in 2006. Polysilicon supply is expected to match demand by 2010, but not before thin film grabs 20 percent of the market.

MSNBC has an article on using molten salt to store energy - a storage mechanism that reportedly only loses 1% of the energy stored per day. There is a discussion at Slashdot

An aerospace manufacturer is developing a way to use molten salt to store solar energy that could produce enough electricity to power 250,000 to 500,000 homes a year. Hamilton Sundstrand, a subsidiary of United Technologies Corp., announced last week that it is working with a California venture capital firm on the project.

The partnership between Hamilton Sundstrand, which makes power systems for the Space Station and Boeing's Dreamliner aircraft, and US Renewables Group in Santa Monica, Calif., would use molten salt to store the sun's heat, which will then be converted to electrical power that could be added to utilities' grids at times of peak demand. ...

Molten salt, a mixture of sodium and potassium nitrate, circulates through a central receiver, is heated by sunlight to more than 1,000 degrees, stored in a tank and dispatched into a steam generator. The steam drives a turbine that generates electricity. The cooled salt re-circulates and the process begins again. The salt loses only 1 percent of its heat per day, which is far better than water and other materials, said Dan Coulom, a spokesman for Hamilton Sundstrand.

Popular Mechanics has an article on the Super Soaker inventor who "aims to cut solar costs in half". His invention is more like a stirling engine than a photovoltaic or CSP set up - but has no moving parts and a claimed conversion efficiency of over 60%. It will be interesting to see how this technology fares out in the wild.

Solar energy technology is enjoying its day in the sun with the advent of innovations from flexible photovoltaic (PV) materials to thermal power plants that concentrate the sun’s heat to drive turbines. But even the best system converts only about 30 percent of received solar energy into electricity—making solar more expensive than burning coal or oil. That will change if Lonnie Johnson’s invention works. The Atlanta-based independent inventor of the Super Soaker squirt gun (a true technological milestone) says he can achieve a conversion efficiency rate that tops 60 percent with a new solid-state heat engine. It represents a breakthrough new way to turn heat into power.

Johnson, a nuclear engineer who holds more than 100 patents, calls his invention the Johnson Thermoelectric Energy Conversion System, or JTEC for short. This is not PV technology, in which semiconducting silicon converts light into electricity. And unlike a Stirling engine, in which pistons are powered by the expansion and compression of a contained gas, there are no moving parts in the JTEC. It’s sort of like a fuel cell: JTEC circulates hydrogen between two membrane-electrode assemblies (MEA). Unlike a fuel cell, however, JTEC is a closed system. No external hydrogen source. No oxygen input. No wastewater output. Other than a jolt of electricity that acts like the ignition spark in an internal-combustion engine, the only input is heat.

Here’s how it works: One MEA stack is coupled to a high- temperature heat source (such as solar heat concentrated by mirrors), and the other to a low-temperature heat sink (ambient air). The low-temperature stack acts as the compressor stage while the high-temperature stack functions as the power stage. Once the cycle is started by the electrical jolt, the resulting pressure differential produces voltage across each of the MEA stacks. The higher voltage at the high-temperature stack forces the low-temperature stack to pump hydrogen from low pressure to high pressure, maintaining the pressure differential. Meanwhile hydrogen passing through the high-temperature stack generates power.

“It’s like a conventional heat engine,” explains Paul Werbos, program director at the National Science Foundation, which has provided funding for JTEC. “It still uses temperature differences to create pressure gradients. Only instead of using those pressure gradients to move an axle or wheel, he’s using them to force ions through a membrane. It’s a totally new way of generating electricity from heat.”

The bigger the temperature differential, the higher the efficiency. With the help of Heshmat Aglan, a professor of mechanical engineering at Alabama’s Tuskegee University, Johnson hopes to have a low-temperature prototype (200-degree centigrade) completed within a year’s time. The pair is experimenting with high-temperature membranes made of a novel ceramic material of micron-scale thickness. Johnson envisions a first-generation system capable of handling temperatures up to 600 degrees. (Currently, solar concentration using parabolic mirrors tops 800 degrees centigrade.) Based on the theoretical Carnot thermodynamic cycle, at 600 degrees efficiency rates approach 60 percent, twice those of today’s solar Stirling engines.

This engine, Johnson says, can operate on tiny scales, or generate megawatts of power. If it proves feasible, drastically reducing the cost of solar power would only be a start. JTEC could potentially harvest waste heat from internal combustion engines and combustion turbines, perhaps even the human body. And no moving parts means no friction and fewer mechanical failures.

Gizmag has a post on solar power that works at night using "nanoantennas" - and this technology is claimed to have a conversion efficiency of 80%. Cryptogon also has some comments - both point to this article from the Idaho National Laboratory.

Idaho National Laboratory (INL) reports that research conducted in conjunction with partners at Microcontinuum Inc. (Cambridge, MA) and Patrick Pinhero of the University of Missouri is promising a method for developing cheap solar energy technology that could be imprinted on flexible materials and still draw energy after the sun has set. The technology uses a special manufacturing process to stamp tiny square spirals, or “nanoantennas”, of conduction metal onto a sheet of plastic and the team estimates individual nanoantennas can absorb close to 80 percent of the available energy in comparison to current commercial solar panels which usually transform less that 20 percent of the usable energy that strikes them into electricity – this is even more impressive than the 30% conversion rate offered by the recently discussed development of nano flakes.

Due to their size – each interlocking spiral nanoantenna is as wide as 1/25 the diameter of a human hair - the nanoantennas absorb energy in the infrared part of the spectrum, just outside the range of what is visible to the eye. Since the sun radiates a lot of infrared energy, some of which is soaked up by the earth and later released as radiation for hours after sunset, nanoantennas can take in energy from both sunlight and the earth's heat, with higher efficiency than conventional solar cells. The new approach, which garnered two 2007 Nano50 awards, was made possible by the boom in nanotechnology, but finding an efficient way to stamp out arrays of atom-scale spirals took a number of years. The INL team says that the antennas might one day be produced like foil or plastic wrap on roll-to-roll machinery and so far they have demonstrated the imprinting process with six-inch circular stamps, each holding more than 10 million antennas.

The nanoantennas could prove to be a more efficient and sustainable alternative to current commercial solar panels, which are made of processed silicon – the supply of which is lagging – and doped with exotic elements to boost efficiency. In contrast the nanoantenna circuits can be made of a number of different conducting metals, and the nanoantennas can be printed on thin, flexible materials like polyethylene. By focusing on readily available materials and rapid manufacturing the team’s aim is to make nanoantenna arrays as cheap as inexpensive carpet. The team says nanoantenna collectors might be used to charge portable battery packs, coat the roofs of homes or even be integrated into polyester fabric.

As exciting as the potential of the technology is, not all the hurdles have been passed yet. While the nanoantennas are easily manufactured, the problem of creating a way to store or transmit the electricity is yet to be solved. Although infrared rays create an alternating current in the nanoantenna, the frequency of the current switches back and forth ten thousand billion times a second - much too fast for electrical appliances, which operate on currents that oscillate only 60 times a second. The team is exploring ways to slow that cycling down and has a patent pending on a variety of potential energy conversion methods. They anticipate they are only a few years away from creating the next generation of solar energy collectors.